1. Field of the Invention
The present invention relates to a liquid crystal display substrate and a fabricating method thereof and a liquid crystal display, in particular to a reflection type liquid crystal display which can realize a low consumption electric power by reflecting an external light and displaying images and a liquid crystal display substrate used therefor and a fabricating method thereof.
2. Description of the Related Art
Among reflection type displays using a light valve for a light modulation, a projection type display using a liquid crystal light valve what is so called a liquid crystal projector can display a very high definition and a large image display, thereby having a possibility to replace CRTs in near future. The projection type display displays images using a transmission type or reflection type liquid crystal light valve. Among them, the conventional reflection type liquid crystal display described in Japanese Laid-open Patent Application No. 8-248425 and the U.S. counterpart Pat. No. 5,739,890 is described with reference to FIG. 9. FIG. 9 shows a schematic cross sectional view of the conventional reflection type liquid crystal light valve. A transistor 104, a detailed picture thereof is omitted, is formed on a silicon substrate 100. A silicon oxide film 102 is formed on the silicon substrate 100 and the transistor 104, and a reflection preventing film 106 using titanium nitride (TiN) is formed on the silicon oxide film 102.
A metal layer 111 is formed on the reflection preventing film 106 as an inter-wire layer via the silicon oxide film 108. A silicon oxide film 102xe2x80x2 is formed on the metal layer 111 as the first insulating film and a reflection preventing film 106xe2x80x2 using TiN is formed on the silicon oxide film 102xe2x80x2. A silicon oxide film 108xe2x80x2 is formed on the reflection preventing film 106xe2x80x2 as the second insulating film and a display electrode 112 which is made of aluminum (Al) and also functions as a light reflecting film is formed thereon.
The display electrode 112 is connected to the metal layer 111 by a connecting conductor 110xe2x80x2 working as a plug electrode, for example, made of tungsten (W) and embedded in a through-hole formed at the silicon oxide film 102xe2x80x2 and silicon oxide film 108xe2x80x2. Further, the metal layer 111 is connected to a source electrode (not shown) of the transistor 104 by a connecting conductor 110 of tungsten embedded in a through-hole formed at the silicon oxide film 102 and silicon oxide film 108. An Al layer is not formed between the adjacent display electrodes 112, and the reflection preventing film 106xe2x80x2 is arranged at least at a lower layer between the display electrodes 112. A glass substrate 116 as an opposing substrate is arranged via a spacer not shown. An opposing electrode 114 is formed on the whole surface of the display electrode 112 side of the glass substrate 116. Furthermore, a liquid crystal 120 is sealed between the opposing electrode 114 and the display electrode 112 at a predetermined cell gap.
The transistor 104 is a FET (field effect transistor) in which, other than the source electrode, a drain electrode connected to data lines and a gate electrode (these are not shown) connected to scanning lines are formed, and the transistor 104 functions as a switching element which applies a voltage applied to data lines when a gate is in the ON state to the display electrode 112.
By changing a transmissivity of the light by changing the direction of liquid crystal molecules 122 in response to a voltage applied between the display electrode 112 and the opposing electrode 114 when the transistor 114 is ON, an incident light from the glass substrate 116 side is reflected by the display electrode 112 and then re-emits from the glass substrate 116 or the light is prevented from reaching to the display electrode 112, thereby a gradation display being performed.
In FIG. 9, though a connection between the display electrode 112 and a source electrode (not shown) of the transistor 104 is made by a drawing-around of the metal layer or the like as a inter-wire layer, an arrangement of this inter-wire layer is not required as long as the relationship of arrangement of the connection between the transistor 104 and the light reflection film 112 coincides.
Further, the silicon oxide films 102, 102xe2x80x2, 108xe2x80x2 and the like which are interlayer insulating films are HDP films formed by a high density plasma (HDP) CVD method and their upper surfaces are performed a planarization process by a polishing process such as a CMP (Chemical Mechanical Polishing) method thereon. In the reflection type liquid crystal display, the planarization of the interlayer insulating film which is a lower layer of the display electrode 112 is important and the surface of the display electrode 112 can be planarized by the planarization of the interlayer insulating film, thereby improving the reflectance of the external light.
Further, the conventional reflection type liquid crystal display shown in FIG. 9 uses TiN as a forming material for the reflection preventing films 106 and 106xe2x80x2. Since TiN has a light absorption function, TiN can prevent the generation of deterioration of the color tone and the like which occurs due to the reflection of the incident light from the gap between the display electrodes 112. It should be noted that in case of the conventional reflection type liquid crystal display, the reflection preventing film 106 is also arranged between the display electrode 112 and the inter-wire layer other than the gap between the display electrodes 112.
In the meantime, TiN used as the forming material for the reflection preventing films 106 and 106xe2x80x2 has a conductivity. Therefore, when the contact holes which connect between the display electrode 112 and the metal layer 111 and between the metal layer 111 and the transistor 104 are directly formed at the reflection preventing films 106 and 106xe2x80x2, TiN which is the forming material for the reflection preventing films 106 and 106xe2x80x2 exposes on the inner faces of the contact holes, so the embedding of the contact holes by the connecting conductors 110 and 110xe2x80x2 results in a problem for shortage of all display electrodes.
Therefore, opening the windows having a diameter larger than a diameter of the contact holes at predetermined positions of the reflection preventing films 106 and 106xe2x80x2, the contact holes are formed in the windows so that the contact holes do not contact to the rims of the windows. For this reason, a patterning for forming the windows at the reflection preventing films 106 and 106xe2x80x2 are required. Further, with respect to the formation of the contact holes, an alignment is required so that the contact holes do not contact with the rims of the windows formed to the reflection preventing films 106 and 106xe2x80x2. At this time, when the windows with the larger diameter are formed at the reflection preventing films 106 and 106xe2x80x2 having an alignment margin to assure the insulation between the connecting conductors 110 and 110xe2x80x2 and the reflection preventing films 106 and 106xe2x80x2, the gap between the display electrodes 112 overlaps the windows of the reflection preventing films 106 and 106xe2x80x2, thereby causing a problem that the incident light from the gap between the display electrodes 112 can not be absorbed at the reflection preventing films 106 and 106xe2x80x2.
An object of the present invention is to provide a liquid crystal display substrate and a fabricating method thereof and a liquid crystal display which can prevent a color tone of a reflection light and the like from deterioration by surely absorbing an incident light from a gap between display electrodes.
The above object is achieved by a fabricating method of a liquid crystal display substrate comprises steps of forming a first insulating film on an electrode connected to switching element, the first insulating film having a more planarized surface than a step difference made by the electrode, forming a insulating reflection preventing film on the first insulating film by a plasma CVD method, forming a through-hole which passes through the reflection preventing film and the first insulating film and exposes a connecting portion of the electrode, and forming a display electrode on an upper layer side of the reflection preventing film, the display electrode having a function for reflecting an incident light and being connected to the electrode via a connecting conductor provided in contact with an inner surface of the through-hole.
Further, above object is achieved by a liquid crystal display substrate comprising a first insulating film provided on an electrode connected to a switching element, the first insulating film having a more planarized surface than a step difference made by the electrode, an insulating reflection preventing film provided on the first insulating film by a plasma CVD method, and a display electrode provided on an upper layer side of the reflection preventing film, the display electrode having a function for reflecting an incident light and connected to the electrode via a connecting conductor provided in contact with an inner surface of a through-hole passing through the reflection preventing film and the first insulating film.